1. Field of the Invention
The present invention relates to a laser treatment apparatus for performing treatment by irradiating an affected part with a laser beam.
2. Description of Related Art
There has been proposed a laser source (a laser oscillator) of a laser treatment apparatus that uses a solid-state laser medium such as an Nd:YAG crystal, and a wavelength converter (a wavelength converting element) such as a nonlinear crystal, and is capable of emitting (oscillating) treatment laser beams of a plurality of different wavelengths (colors) in a visible region. Such laser source includes resonance optical systems for emitting the treatment laser beams of different wavelengths (see U.S. Pat. No. 6,636,537 corresponding to Japanese unexamined patent publication 2002-151774).
As a control system for driving a laser source, commonly used is a so-called “power on-demand” system in which a necessary amount of electric current is applied to the laser source only when needed and the laser source emits an amount of a laser beam required to irradiate a needed amount of the laser beam to an affected part. In the laser source including the resonance optical systems for emitting laser beams of different wavelengths, each resonance optical system has to be adjusted to stably provide the emission amount of a laser beam of every wavelength needed for treatment. The emission amount of a laser beam of a certain wavelength from such laser source can be proportional in one-one relation to the amount of applied electric current, whereas the emission amount of a laser beam of another wavelength is not proportional in one-one relation to the amount of applied electric current as shown in FIG. 8. For this reason, the laser treatment apparatus having such laser source cannot adopt the power on-demand system.
As a measure corresponding to above, it is conceivable that the emission amount of a laser beam by the laser source is set to be consistently constant and further the irradiation amount of the laser beam is controlled by use of an attenuating means such as a polarization member or a ½ wave member. If the emission amount of the laser beam is set to be consistently constant, however, it is likely to place a load on optical elements disposed in the resonance optical systems and the laser source. This may shorten their useful lives.